The present invention relates to mineral recovery processes and particularly but not only flotation of valuable minerals which use oxygen as a conditioning and/or flotation gas.
The use of flotation processes to recover valuable minerals is well known in the art. The control and optimisation of these processes, however, can sometimes be hit or miss.
A mineral recovery process such as froth flotation which may work extremely well in one geographic location and with one particular type of ore but may be entirely unsuitable in another location due to the different reactivities of the ores.
Further, even at one location and one ore body the reactivity of the ore may change on an hourly, daily or weekly basis. There is significant variability in the characteristics of the ore processed by flotation at any particular mine. Changes are unpredictable and are caused by: ore bodies that are not homogenous, mining practices, stockpiling, crushing, and milling conditions. Even slight changes in the ore""s characteristics can upset the delicate balance in the flotation cells and have a substantial negative impact on the recovery of the valuable sulphide mineral.
Researchers have established that most sulphide minerals require some oxygen for complete flotation. There are three collector reaction mechanisms generally accepted for xanthate type collectors (the most common collector type used) that lead to making valuable minerals floatable:
Electrostatic Collector Attraction
MeS+H2O+2O2=Me(H2O)2++SO42xe2x88x92
The ionically charged collector attracts to the mineral surface
Chemisorption
1) MeS+2O2=MeSO4 
2) MeSO4+CO32xe2x88x92=MeCO3+SO42xe2x88x92
3) MeCO3+2X=MeX2+CO32xe2x88x92
Metal xanthate layer builds up on mineral surface.
Electrochemical Oxidation
1) 2Xxe2x88x92+1/2 O2+H2O=X2+20Hxe2x88x92
2) MeS+X2=(MeS)X2ads 
The collector is initially oxidised and then attaches to the mineral surface.
Oxygen is required for each of the collector mechanisms recognised. Oxygen is the principal electron acceptor. Oxidising conditions favour reaction with xanthate type collectors including dithiophosphates. Thiocarbamate and thiourea collector actions also require oxygen for complete flotation.
Many flotation pulps are oxygen deficient. Milling produces a reducing environment. Grinding media and minerals corrode. Oxygen in the pulp is consumed. Some minerals present in the ore can be significant oxygen consumers eg pyrrhotite, marcasite, pyrite.
Valuable sulphide minerals are also prone to over oxidation that can reduce flotability. Previously, where an oxygen deficiency has been recognised air was used as the oxidation gas. Due to its low dissolved oxygen saturation point (5-8 ppm), the danger of over oxidation was minimal. However, the applicant has discovered that the intensity of oxidative conditioning in the full scale application can usually only be achieved by using an oxygen-rich gas which has a higher saturation point. This in turn may lead to over oxidation over the valuable mineral, if the addition of the oxidation gas is not adequately controlled.
In the flotation of sulphide ores it has been found that the oxidising environment in the pulp, as measured by oxidationxe2x80x94redox potential (or Eh) has a strong influence on the flotation result. Eh has frequently been measured but not often used as a control parameter. The reasons for this include unreliable electrodes, changes in Eh being more attributable to changes in pH, and the difficulty in controlling Eh by some reagent addition.
Dissolved oxygen (DO) concentration in the pulp has also been tried as an indicator of the status of the flotation process. Air has been occasionally used as an aeration gas to raise the dissolved oxygen concentration of the slurry. Measurement of dissolved oxygen concentration though does not give sufficient information on whether ore oxygen gas flow requirements have been optimised.
The applicant has found that the oxidative conditioning step in the ACTIFLOAT process, which is subject of Australian patent no 670,163 and application no 37917/95 and several overseas patents and co-pending applications, provides substantial improvements over conventional flotation methods. There is no doubt that with many ores an oxidative conditioning step conducted prior to or simultaneously with the flotation step increases the recovery of the valuable mineral over conventional treatment.
Current and potential users of the process, however, have indicated that it would be useful to have in place methods and equipment to rapidly and accurately determine the oxygen gas flow requirements of the slurry being processed, fluctuations in the make up of the ore will change the oxygen gas flow requirements. Optimising oxygen addition is an important component of the overall efficiency of the ACTIFLOAT process.
Equally, some ores may not be susceptible to oxidative conditioning or alternatively such conditioning may in fact be detrimental to mineral recovery. In such instances it would be beneficial to determine whether the oxygen gas flow requirements of such ores are negligible and thereby characterise the flotability of the slurry.
The present invention seeks to provide a method for controlling a mineral recovery process which overcomes at least some of the disadvantages of the prior art or provides a commercial alternative thereto.
In a broad aspect, the present invention provides a method of optimising a mineral flotation recovery process comprising extracting a representative sample of a slurry containing the mineral to be recovered, treating the sample with an oxidising gas, measuring one or more parameters before and/or after said oxidative treatment wherein the change in said parameter(s) is indicative of the flotability of the minerals contained in the slurry, characterising the slurry as a function of said measured parameter(s), and controlling the mineral recovery process in accordance with said slurry characteristic.
The present applicant has found that the inventive method is particularly suitable for optimising the ACTIFLOAT process ie a process which has oxidative conditioning of the slurry. It will be recognised, however, that the inventive method is also suitable for other flotation processes such as MAXIFLOAT and CLEANFLOAT both of which use non-oxidising gases to condition or float the desired minerals.
The present invention provides a mechanism for optimising a mineral flotation recovery process in several ways, namely:
a) characterising a slurry by providing a measure of the flotability of the minerals contained therein after an oxidative gas treatment,
b) determining the effect of various control regimes on the slurry and indeed the entire mineral recovery process eg what effect do different dissolved oxygen, pH, electrochemical potential levels, different mixing times, different intensities of mixing etc have on the flotation recovery of the valuable minerals, and
c) providing an historic record of the correlation between the effect of different parameter alterations, ore types etc and the flotability of the minerals contained within the slurry thereby allowing an operator to predict what control parameters are required to optimise mineral recovery.
In another broad aspect, the present invention provides an apparatus for optimising a mineral flotation recovery process comprising means for extracting a representative sample of the slurry, means for treating the sample with the oxidising gas, means for measuring one or more parameters before and/or after said oxidative treatment wherein the change in said parameter(s) is indicative of the flotability of minerals contained in the slurry, and means to determine a slurry flotability characteristic as a function of said measured parameter(s), said apparatus being operatively linked with said mineral flotation recovery process to thereby control said mineral flotation recovery process in accordance with said slurry characteristic.
The parameters to be measured may be selected from any one of dissolved oxygen concentration, electrochemical potential, pH, temperature, chemical species in solution, mineral content, mineral surface composition and mineral surface properties. It will be appreciated by persons skilled in the art that the change in these parameters is indicative of the flotability of the minerals contained within the slurry.
In accordance with the invention, as many parameters of the slurry as are required are measured to provide a reliable characterisation of the flotability of the contained minerals in the slurry. By the phrase xe2x80x9cindicative of the flotability of minerals contained in the slurryxe2x80x9d we mean indicative of the flotability of minerals in the slurry per se, but also indicative of the flotability of the minerals in slurry when subjected to the respective mineral recovery process. A mineral slurry may be perfectly flotable in one process yet difficult to float in another process where the changes in process parameters are quite minor.
The list of parameters mentioned above is not meant to be exhaustive. One of the advantages of the present application is that the type and number of parameters to be measured may be tailored by an individual operator to suit the particular mineral recovery process. For instance, if consistent water supply is not reliable and water must be obtained from different sources, it may also provide helpful to measure various parameters of the slurry water to determine its effect on the flotability of the slurry.
Another advantage of the present invention is its ability to apply a series of experiments to the representative sample under conditions which do not replicate the mineral recovery process but which serve to optimise the mineral recovery process. To explain, in an embodiment where the mineral recovery process includes an oxidative conditioning step, it may be determined that the oxidative gas treatment applied to the representative sample should replicate the oxidative conditioning step in the mineral recovery process. Alternatively, a series of experiments may be applied to the representative sample under conditions which do not replicate the oxidative conditioning step. These experiments may include different oxidising gas types, different mixing times, different intensities of mixing and different temperatures.
In some mineral flotation recovery processes, little or no oxidative conditioning is required or applied. The inventive method and apparatus, however, is still useful in characterising the slurry. The tests applied to the representative sample may be used to confirm whether or not the mineral recovery process may be optimised by including an oxidative conditioning step.
In this way, an operator can experiment with the current slurry passing through the mineral recovery process without interrupting or upsetting the mineral recovery process itself. It will be appreciated, that this is a very useful mechanism for applying alternative process parameters to optimise the mineral recovery process.
The method and apparatus has been discussed above as being used to optimise a mineral recovery process. It will be appreciated, however, that the method and apparatus may equally be used simply to characterise a slurry by determining the flotability of its contained minerals. The characterisation of the slurry can be used for a number of purposes other than optimisation of the mineral recovery process. For example, it is useful to determine which ore is more easily flotable or more compatible with current process equipment and limitations attached thereto. An example may be where it is intended to change the ore body from which the slurry originates. Clearly there would be significant advantages in being able to test several alternative ore bodies to determine their compatibility with current process equipment.
In a third aspect, the present invention provides a method of characterising the flotability of a slurry in a mineral flotation recovery process comprising extracting a representative sample of the slurry to be floated, treating the sample with an oxidising gas, measuring one or more parameters before and/or after said oxidative treatment wherein the change in said parameter(s) is indicative of a flotability of the minerals contained in the slurry, and characterising the slurry as a function of said measured parameter(s).
In a fourth aspect, the present invention provides an apparatus for characterising the flotability of a slurry in a mineral recovery process comprising a slurry feed to extract and provide a representative sample of the slurry to be floated, an oxidising gas supply to contact and treat the sample with an oxidising gas, an analysis means to measure one or more parameters both before and/or after said oxidative treatment wherein the change in said parameter(s) is indicative of the flotability of the minerals contained in the slurry, and a calculation means to determine the flotability characteristic of the slurry as a function of said measured parameter(s).
Unless the context clearly requires otherwise, throughout the description and the claims, the words xe2x80x98comprisexe2x80x99, xe2x80x98comprisingxe2x80x99, and the like are to be construed in an inclusive as opposed to an exclusive or exhaustive sense; that is to say, in the sense of xe2x80x9cincluding, but not limited toxe2x80x9d.